1. Field of the invention
This invention relates generally to white-balance adjusting apparatuses and, more particularly, to a white-balance adjusting apparatus which provides a certain gain to a color information signal to thereby adjust the white balance.
2. Description of the prior art
FIG. 16 illustrates a color distribution, in which the area represented by hatching (draw-in area) corresponds to a monochromatic color while the outside of the draw-in area to a chromatic color. There is distribution of Mg (magenta) in a first quadrant of a plane defined by the R-Y and B-Y axes. In a second quadrant, R (red) and Ye (yellow) are distributed. In a third quadrant G (green) is distributed, and in a fourth quadrant Cy (cyan) and B (blue) are distributed.
Such color temperature charts have being used in the conventional white-balance adjusting apparatuses applied for digital cameras in order to adjust the white balance in a taken subject image. That is, a taken subject image is first divided into a plurality of partial images, and then a color evaluation value is determined for each of the partial images. Next, activation is made for the color evaluation values included in the draw-in area. Then, the gain is controlled by converging the mean values of the activated color evaluation values to an intersection of the R-Y axis and the B-Y axis.
However, the color evaluation value is varied depending upon a lens opening or shutter speed (exposure amount) during taking a picture. That is, the change of exposure amount also causes change in the amount of light illuminated to the image sensor. According to the color distribution chart of FIG. 16, because the Y signal related to light amount is reflected in the color evaluation value, the color evaluation value is varied due to the exposure amount. Consequently, the conventional digital cameras encounters phenomenon that the color evaluation value with a certain exposure amount exist in the draw-in area to enable proper adjustment of white balance while the color evaluation value with another exposure amount is outside the draw-in area resulting in poor adjustment of white balance.
Meanwhile, where taking a picture of a subject including a human skin, if the color evaluation value on the human skin part is invalidated, the skin color is prevented from changing largely. However, the color evaluation value suffers variation due to the exposure amount as mentioned above. Accordingly, the prior art could not invalidate the color evaluation value only in a human skin part. Consequently, if taking a picture of a subject including much a human skin, the skin in color will possibly turn into pale.
Therefore, it is a primary object of the present invention to provide a white-balance adjusting apparatus capable of preventing a skin color from turning into another color as effective as possible.
According to the present invention, a white-balance adjusting apparatus for providing an optimal gain to a color information signal corresponding to a subject image to thereby adjust white balance while suppressing a skin color component contained in the color information signal from changing, comprises: a color evaluator for evaluating colors of a predetermined plurality of portions of the subject image based on the color information signal; a luminance evaluator for evaluating luminances of the predetermined plurality of portions based on the color information signal; a remover for removing a plurality of luminance evaluation components given by the luminance evaluator respectively from a plurality of color evaluation components provided by the color evaluator; a table having a first numeral related to a monochromatic color and a second numeral related at least to a skin color; a detector for detecting from the table respective numerals related to the components removed by the remover; and an optimal gain calculator for calculating the optimal gain based on the numerals detected by the detector and the color evaluation components.
The color evaluator evaluates colors in a predetermined plurality of portions of a subject image based on a color information signal corresponding to the subject image, and determines a plurality of color evaluation components. The luminance evaluator evaluates the predetermined plurality of portions based on the same color information signal. The remover removes a plurality of luminance components respectively from a plurality of color evaluation components to determine a plurality of removal components. On the other hand, the table has a first numeral related to a monochromatic color and a second numeral related at least to a skin color. The detector detects, from the table, numerals related respectively to the removal components determined by the removing means. The optimal gain is calculated by the optimal gain calculator, based on the numerals detected by the detector and the color evaluation components. The optimal gain is provided to the color information signal for the subject image, thereby adjusting white balance while suppressing the skin-color component contained in the color information signal from changing.
In one aspect of the invention, the optimal gain calculator first calculates a first gain based on the color evaluation components and then gives weighting to each of the first gain and a predetermined second gain. This provides the optimal gain.
In a preferred embodiment of this aspect, the second gain is always equal to or smaller than the first gain. In the weighting processing, the weighting to the second gain is increased with increase of a ratio of the second numeral to the detected numerals.
In another preferred embodiment of this aspect, when determining the first gain, the removal component related to the monochromatic color and the skin color is specified from among the removal components, and activation is made for the color evaluation component corresponding to the specified removal component. The first gain is calculated based on the activated color evaluation component.
In another aspect of the invention, the second numeral is related also to green.
In another aspect of the invention, the table further has a third numeral related to other colors than the monochromatic color and the skin color. That is, the table has the first, second and third numerals. The first numeral is greater than the second numeral, and the second numeral is greater than the third numeral. A multiplier multiplies the detected numerals respectively by the color evaluation components. The optimal gain is calculated based on a plurality of multiplication values given by the multiplier.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.